Our invention is adapted to be used in a multiple ratio planetary transmission situated in a vehicle driveline having an internal combustion engine with a throttle control and a hydrokinetic torque converter situated between the engine and input elements of the gearing.
The gearing of the transmission disclosed in this specification comprises two simple planetary gear units arranged in a manner similar to the gearing arrangement of the well known Simpson gear set. Located between the turbine of the torque converter and the input elements of the Simpson gearing is a third simple planetary gear unit with a friction clutch adapted to connect two elements of the third gear unit together for rotation in unison. A friction brake also is used for anchoring a reaction element of the third planetary gear unit. An overrunning coupling establishes one-way torque flow between two elements of the gearing. The brake is arranged in series relationship with respect to the clutch.
A second overrunning coupling in a gear unit of the Simpson gearing is used for the purpose of establishing a non-synchronous ratio shift. Forward engagement is achieved by engaging a forward clutch on a shift from neutral to a drive state. Similarly, a separate reverse engagement clutch is used to establish a torque flow path for reverse. In each instance, turbine speed is used as a feedback signal to initiate the start of the forward or reverse engagement.
Ratio changes on a downshift from the second ratio to the first ratio, is achieved in our improved transmission by controlling the engagement of an overrunning clutch. The overrunning clutch is arranged with respect to a friction brake to provide a reaction torque flow path associated with the intermediate ratio as the first ratio is established. The brake disengagement is accomplished with a closed loop control so that harshness is avoided as the overrunning elements of the reaction torque flow path engage. This is in contrast to prior art arrangements, such as that shown in U.S. Pat. No. 5,157,608, where a non-synchronous shift using overrunning couplings is achieved without the cushioning effect made available by the present invention as the associated friction brake is released.
The disclosed embodiment of the transmission includes also a torque converter controller for a torque converter that has a single converter feed passage and a single converter flow return passage. Such converters are distinguishable from converters of the kind shown, for example, in U.S. Pat. No. 5,305,663 where a converter bypass clutch feed passage acts in cooperation with two other distinguishable feed passages, one acting as a flow return and the other acting as a flow delivery to the torus circuit of the converter. In the case of the converter shown in the '663 patent, continuous flow is achieved through the converter regardless of whether the clutch is engaged or released.
Portions of the clutch strategy of the present invention are common to the teachings of U.S. Pat. No. 5,029,087, issued to Ronald T. Cowan, Roger L. Huffmaster and Pramod K. Jain. As in the case of the converter control of the '087 patent, our present invention includes a controller for continuously monitoring the actual converter slip and comparing that actual value to a desired value. Any error that is detected by the controller will result in calculation of a new target slip. During the engagement time of the converter clutch, the error will continuously change and the magnitude of that error will be continuously monitored. In each instance, a new target slip is calculated. This process continues until the actual slip approaches the target value.
The pressure buildup system includes a variable force solenoid that communicates with a regulated line pressure passage which is pressurized in conventional fashion by a positive displacement pump driven by the engine. The variable force solenoid responds to a control signal developed by the electronic pressure control strategy to produce an output current that makes it possible for the variable force solenoid to develop a pressure which is referred to in this specification as the EPC pressure.
The EPC pressure is distributed to an EPC booster valve which develops a pressure called the EPC boost pressure. That pressure acts on the main regulator valve to change the regulating characteristics of the main regulator valve so that control of the brake and clutch capacity can be achieved for stall conditions for all gear ratios. It is not necessary to provide an additional solenoid to effect changes in the main regulator valve line pressure.
It is possible to calibrate the EPC boost valve in such a way that higher boost pressure in the line pressure circuit can be obtained while providing the optimum line pressure for valve control during normal operations other than stall. The regulator can be calibrated, therefore, to provide appropriate pressure for ratio changes without consideration for the separate calibration that be required to effect an increased servo capacity for stall purposes.
The manual valve that is under the control of the vehicle operator can be shifted to a second ratio position or a low-speed ratio position manually, thereby overruling the automatic upshifts and downshifts that occur when the manual valve is adjusted to the normal automatic drive range position. If there is a failure in the electronic pressure control pressure, the main regulator valve will not lose capacity since provision is made for pressurizing the main regulator valve with the pressure that is developed for purposes of the operation of the transmission in the second drive range or the first drive range.
The pressure boost system is capable of adjusting the capacity of the main regulator valve for both upshifts and downshifts under stall conditions, thereby varying the capacities of the clutches without the need for having conventional accumulators to soften the engagement of the clutches.
The pressure buildup system includes separate solenoid regulator valves. One solenoid regulator valve develops a supply pressure for a pulse width modulated solenoid that is used for the purpose of controlling the converter clutch. The other solenoid regulator valve is used to supply pressure to the on-off solenoids that are used to effect ratio changes. Thus, the input pressure for the on-off solenoids can be reduced. That reduces the cost and increases the reliability of the on-off solenoids for controlling ratio changes. Further, better calibration and control of the solenoids can be achieved if the multiple functions required of the converter solenoid and the on-off solenoid for the shift valves is achieved using independent solenoid regulators.
The improved pressure buildup system of our invention controls the engagement of the reverse clutch by ramping the electronic pressure control pressure by using a clutch pressure reverse modulator. The modulator establishes initially pressures lower than the normal idle line pressure and then ramps the pressure upward to increase clutch capacity without the necessity for providing the usual accumulator assembly with a variable volume and accumulator spring. Engagement of forward drive from park or neutral also is cushioned with an electronic accumulator system without the necessity for using a conventional variable volume accumulator to effect a gradual pressure buildup in the forward engagement clutch.
In the case of a forward engagement, the forward engagement valving includes a clutch pressure modulator valve for forward, which corresponds to the clutch pressure modulator valve for reverse described previously. The valve system for forward engagement provides low pressure values less than normal idle line pressure. The forward drive clutch pressure is gradually ramped up to achieve good engagement quality using the output pressure of the clutch pressure modulator valve for forward. The input to the clutch pressure modulator valve for forward is the electronic pressure control (EPC) made available by the variable force solenoid that is under the control of the microprocessor. As in the case of reverse engagement, the accumulator effect for forward engagement is achieved entirely electronically.